Laminated assembly of polycarbonate and polyacrylate resin sheets and method of making the same

ABSTRACT

Transparent globe for street lighting luminaires comprises a laminated assembly of superposed sheets of polycarbonate resin and polyacrylate resin having an ultraviolet absorbing compound incorporated preferably in the polyacrylate resin sheet.

United States Patent Osteen May 9, 1972 [54] LAMINATED ASSEMBLY OFPOLYCARBONATE AND POLYACRYLATE RESIN SHEETS AND METHOD OF MAKING THESAME [72] Inventor: Mitchell M. Osteen, Zirconia, N.C.

[73] Assignee: General Electric Company [22] Filed: Oct. 28, 1968 21Appl. No: 771,107

[52] U.S.Cl ..161/1, 156/306, 161/183,

161/252, 240/25 [51] Int. Cl. ..l-l0lk 5/00, 1332b 27/30 [58] FieldoiSearch ..161/1,6, 183,247,252; 156/306; 240/25 [56] References CitedUNITED STATES PATENTS Dietzelet a1. ..161/183X Ringler ..161/183 X2,774,697 12/1956 Koblitz ..161/183 2,787,568 4/1957 Koblitz 161/1833,309,220 3/1967 Osteen..... 117/333 3,320,116 5/1967 Tocker 161/2523,348,035 10/1967 Franklin et a1 ..240/25 3,388,035 6/1968 Mattimoe eta1... ..161/183 3,420,679 1/1969 Gifford et al.... ..161/183 X 3,435,2023/1969 Jabl0nski.... ..240/25 3,457,104 7/1969 Bristol ...l 17/138.83,520,768 7/1970 Peilstocker et a1 ..161/183 X Primary E.\'aminerHaroldAnsher Attorney-Sidney Greenberg, J. Wesley Haubner, Frank L. Neuhauser,Oscar B. Waddell and Melvin M. Goldenberg [5 7] ABSTRACT Transparentglobe for street lighting luminaires comprises a laminated assembly ofsuperposed sheets of polycarbonate resin and polyacrylate resin havingan ultraviolet absorbing compound incorporated preferably in thepolyacrylate resin sheet.

1 1 Claims, 3 Drawing Figures LAMINATED ASSEMBLY OF POLYCARBONATE ANDPOLYACRYLATE RESIN SHEETS AND METHOD OF MAKING THE SAME The presentinvention relates to composite plastic products and the method of makingthe same, and more particularly relates to such products which aresuitable for use as light transmitting globes or refractors for streetlighting luminaires or other lighting fixtures. I

It is an object of the present invention to provide a composite lighttransmitting plastic product having good impact resistant properties andhigh operating temperature capabilities coupled with high resistance todegradation by ultraviolet light.

It is another object of the invention to provide a laminated product ofthe above type which is readily fabricated for use in a variety ofapplications, and which is especially suitable for light transmittingglobes or refractors of luminaires and the like.

It is a particular object of the invention to provide a lighttransmitting globe of the above type for use in street lightingluminaires having a light source from which some ultraviolet radiationis emitted and which are installed in areas where the globes are subjectto breakage due to vandalism or other hazardous conditions.

Other objects and advantages will become apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention in one of itsaspects relates to a composite plastic material comprising a sheet ofpolycarbonate resin having superimposed thereon a sheet of polyacrylateresin in intimate adherence thereto, at least one of the resin sheetshaving an ultraviolet absorbing compound incorporated therein.

The invention will be better understood from the following descriptiontaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a view in elevation, partly broken away, of a street lightingluminaire having a transparent laminated refractor embodying theinvention;

FIG. 2 is an enlarged cross-sectional view of a portion of the laminatedrefractor of the FIG. 1 device; and

FIG. 3 is a diagrammatic showing of a method for making the laminatedsheet of the invention.

Referring now to the drawing, and particularly to FIG. 1, there is showna street lighting luminaire comprising a housing 1 in which are mounteda reflector 2 and a lamp 3, and a light transmitting globe or refractor4 mounted in a bottom door 5 for enclosing the reflector and lamp.Bottom door 5 is hingedly secured at its rear end to housing 1 anddetachably secured at its front end thereto by latch 6.

Lamp 3 is typically a gaseous discharge lamp, such as a mercury orsodium vapor lamp, fluorescent lamp, or other light source which inoperation emits appreciable amounts of ultraviolet radiation. Whileconventional refractors of glass usually employed for such luminairesare ordinarily not adversely affected by exposure to ultraviolet rays,organic polymeric (i.e., synthetic plastic) materials generally aredegraded to some extent by such rays. Hence, although the use of plasticrefractors is often desirable in order to obtain the advantages oflightness, economy and other favorable characteristics, various adverseeffects have been encountered in such use. Their degradation resultingfrom exposure to ultraviolet radiation manifests itself in yellowing orother discoloration, embrittlement, and loss of other initially goodphysical properties. A particular resin material which is otherwisedesirable for use in luminaire refractors is polycarbonate resin, inview of its good light transmitting properties coupled withexceptionally high impact strength and thermal resistance. However, thisplastic material is likewise adversely affected by exposure toultraviolet radiation.

In accordance with the invention, this difficulty is overcome byproviding a laminated assembly of a polycarbonate resin sheet and apolyacrylate resin sheet, wherein an ultraviolet light absorbingcompound is incorporated in the polyacrylate resin sheet. Such alaminated assembly is shown in FIG. 2, wherein a portion of therefractor 4 of FIG. 1 is shown in cross-section, the assembly comprisingan outer sheet 4a of polycarbonate resin having a thin polyacrylateresin sheet 4b intimately bonded thereto. Polyacrylate resin sheet 4bhas dispersed therein a suitable ultraviolet absorbing compound 40, asmore fully disclosed' below. As will be seen, the polyacrylate resinsheet 4b is arranged on the inside of the refractor so as to interceptthe ultraviolet rays from lamp 3 before they can enter the polycarbonateresin sheet 40.

The polycarbonate resins used in the practice of this invention are wellknown in the art and may be defined as high molecular weight aromaticcarbonate polymers which may be prepared by reacting a dihydric phenolwith a carbonate precursor such as phosgene, a. haloformate or acarbonate ester. Such carbonate polymers are characterized by recurringstructural units of the formula where A is a divalent aromatic radicalof the dihydric phenol employed in the polymer producing reaction.Details of such carbonate polymers and the method of making them arefound in US. Pat. No. 3,309,220 Osteen, which is incorporated byreference herein.

The term polyacrylate as used herein is meant to embrace within itsscope those polymers or resins resulting from the polymerization of oneor more acrylates such as, for example, methyl acrylate, ethyl acrylate,butyl acrylate, 2-ethylhexyl acrylate, etc., as well as themethacrylates such as, for instance, methyl methacrylate, ethylmethacrylate, butyl" methacrylate, hexyl methacrylate, etc. Copolymersof the above acrylate and methacrylate monomers are also included withinthe term polyacrylate" as it appears herein. The polymerization of themonomeric acrylates and methacrylates to provide the polyacrylate resinsuseful in the practice of the invention may be accomplished by any ofthe well-known polymerization techniques.

The polyacrylate resin sheet 4b has incorporated therein an ultravioletlight absorbing compound which may be any suitable one of the knowncompounds of this type. Such compounds are disclosed, for' example, inthe aforementioned Osteen patent, and includes substituted derivativesof benzophenone and of benzotriazole, among other compounds. Theultraviolet absorbing compound may be incorporated in the polyacrylateresin by addition of the absorber into the bulk material, referred to asbulk stabilization, or by applying the absorber as a coating on thesurface of the polyacrylate resin sheet. While it is preferred toincorporate the ultraviolet absorbing compound in the polyacrylate resinsheet, the invention includes within its scope the use of theultraviolet absorber in either or both of the polyacrylate resin orpolycarbonate resin sheets. The ultraviolet light absorbing compound maybe of types other than those mentioned above, as, for example, compoundsor materials which are capable of transforming the ultraviolet light tolight of other wavelengths or to other forms of energy which areinnocuous or even beneficial to the properties of function of theplastic refractor. Such compounds and materials accordingly are intendedto be included in the meaning of ultraviolet absorbing compound as usedherein.

In work done in connection with the invention, a 15 mil thick sheet ofpolymethylmethacrylate containing an ultraviolet stabilizer washeat-pressure fused to a three-sixteen inches thick sheet ofpolycarbonate resin in a laboratory press, using a total pressure of5,000 lbs. over an area of 6.25 sq. in. at a temperature of 155 C. Thepress heater was then turned 0E, and the entire mass cooled bycompressed air to C while the aforementioned pressure was maintained.The polycarbonate-polyacrylate laminate thus made was then removed fromthe press.

Two laminated units prepared by the above described procedure were cutin half and the resulting four samples were numbered respectively 1,2,3and 4. Percent transmission curves in wavelengths from 350 to 650 muwere recorded, and

the initial yellowness factor for each sample was calculated by where Trepresents the percent transmission at the subscript V I wavelength inmg. of the sample, as compared to air. The initial yellowness factorswere found as follows:

Sample 1 l4 Sample 2 Sample 3 12 Sample 4 12 Sample 1 11 Sample 2 31Sample 3 10 Sample 4 31 It is evident from these results that thelaminated products arranged with the polyacrylate resin sheet facing theultraviolet radiation source exhibited much greater resistance todiscoloration than those not so arranged. I

A laminated polycarbonate-polyacrylate product ofthe described type maybe produced by a variety of methods. Sheet stock for subsequent vacuumforming could be produced by employing two extruders and pressing theextruded sheets of the respective resins together while still hot.injection molding processes may also be found useful in providing such alaminated composite sheet of desired configuration.

An example of an extruding process is illustrated in FIG. 3, whereinextruder 7 produces a sheet of polycarbonate resin and extruder 8produces a sheet of polyacrylate resin. Typically, rollers 9 are at atemperature of about 150 C., while rollers 10 are about 100 C. Heaters11 and 12 respectively span the width of the extruded sheets and asshown are arranged near the point of contact of the converging sheets,and are placed adjacent the facing surfaces of the plastic sheets so asto heat these surfaces for fusing the same. Heater ll heats the innersurface of the polycarbonate sheet to a temperature of about 150 to 300C., while heater l2 heats the polyacrylate sheet surface to atemperature of about 100 to 200 C. Rollers l3 and 14 press the thusheated plastic sheets together with sufiicient pressure, e.g., in therange of about 5005,000 psi to form a tightly adherent, laminatedcomposite sheet.

With such a sheet used for a luminaire refractor as shown and describedin connection with FIGS. 1 and 2, the outer layer of polycarbonate resinprovides high impact strength and thermal stability for firm support andprotection of the polyacrylate resin film, while the latter film with UVabsorber therein will intercept the ultraviolet radiation from the lampto protect the polycarbonate layer from the'deleterious effects of suchradiation.

While a typical laminated assembly is composed of a sheet ofpolyacrylate resin and a sheet of polycarbonate resin, the inventionincludes within its scope a lamination comprising polyacrylate resinsheets with UV absorber therein on opposite sides of, the polycarbonateresin sheet, whereby the latter sheet is protected on both sides fromultraviolet rays, which may, for example, emanate from a lamp on oneside of the lamination and from the sun on the other side.

It will also be understood that the laminated product of the inventionwill find a variety of applications in addition to that of streetlighting, as for example for window glazing, auto tail lights, and otheruses where exposure to ultraviolet light, elevated temperature, and riskof breakage may be a problem.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A composite material comprising a laminated assembly of superposedsheets respectively consisting essentially of aromatic polycarbonateresin and polyacrylate resin.

2. A material as defined in claim 1, wherein one of said sheets hasincorporated therein an ultraviolet radiation absorbing compound.

3. A material as defined in claim 1, wherein said polyacrylate resinsheet has an ultraviolet radiation absorbing compound incorporatedtherein.

4. A material as defined in claim 3, and a light source which emitsultraviolet radiation arranged adjacent said material.

5. A device as defined in claim 4, wherein said laminated assembly isarranged with the polyacrylate resin sheet facing said light source.

6. A device as defined in claim 5, wherein said light source is mountedin a luminaire and said laminated assembly is in the form of a lighttransmitting globe covering said light source.

7. A device as defined in claim 1, wherein the polycarbonate resin sheetis sandwiched between polyacrylate resin sheets.

8. A device as defined in claim 7, wherein the polyacrylate resin sheetscontain an ultraviolet absorbing compound.

9. A method of making a laminated composite plastic sheet whichcomprises forming separate sheets of an aromatic

2. A material as defined in claim 1, wherein one of said sheets hasincorporated therein an ultraviolet radiation absorbing compound.
 3. Amaterial as defined in claim 1, wherein said polyacrylate resin sheethas an ultraviolet radiation absorbing compound incorporated therein. 4.A material as defined in claim 3, and a light source which emitsultraviolet radiation arranged adjacent said material.
 5. A device asdefined in claim 4, wherein said laminated assembly is arranged with thepolyacrylate resin sheet facing said light source.
 6. A device asdefined in claim 5, wherein said light source is mounted in a luminaireand said laminated assembly is in the form of a light transmitting globecovering said light source.
 7. A device as defined in claim 1, whereinthe polycarbonate resin sheet is sandwiched between polyacrylate resinsheets.
 8. A device as defined in claim 7, wherein the polyacrylateresin sheets contain an ultraviolet absorbing compound.
 9. A method ofmaking a laminated composite plastic sheet which comprises formingseparate sheets of an aromatic polycarbonate resin and a polyacrylateresin, and joining said sheets together in superposed relation.
 10. Themethod as defined in claim 9, wherein an ultraviolet absorbing compoundis incorporated in the polyacrylate resin sheet.
 11. The method asdefined in claim 9, wherein said sheets are fused together byapplication of heat and pressure.